Lightning generation in moist convective clouds and constraints on the water abundance in Jupiter

TL;DR

This study uses Juno observations to model lightning in Jupiter's moist convection, constraining water abundance and showing that lightning occurs within a specific water abundance range, including subsolar levels.

Contribution

It introduces a model linking lightning generation to water and ammonia levels in Jupiter's atmosphere, based on extensive observational data.

Findings

Lightning occurs at various pressure levels, including below the water cloud base.

A solar or subsolar water abundance range is consistent with observed lightning.

Ammonia stabilizes liquid water at sub-freezing temperatures, enabling lightning.

Abstract

Recent Juno observations have greatly extended the temporal and spatial coverage of lightning detection on Jupiter. We use these data to constrain a model of moist convection and lightning generation in Jupiter's atmosphere, and derive a roughly solar abundance of water at the base of the water cloud. Shallow lightning, observed by Juno (Becker et al., 2020, Nature, 584, 55-58) and defined as flashes originating at altitudes corresponding to pressure less than 2 bars, is reproduced, as is lightning at a deeper range of pressures, including those below the water cloud base. It is found that the generation of lightning requires ammonia to stabilize liquid water at altitudes corresponding to sub-freezing temperatures. We find a range of local water abundances in which lightning is possible, including subsolar values of water--consistent with other determinations of deep oxygen abundance.